Closed-cell rigid polyurethane foams are useful for insulating appliances and buildings due to their low thermal conductivity and dimensional stability at low densities. Rigid polyurethane (PU) foams and polyurethane-polyisocyanurate (PIR) foams are conventionally prepared by reacting appropriate polyisocyanates and active hydrogen containing polyols in presence of suitable physical blowing agents. Physical blowing agents produce their blowing effect by physical expansion rather than by chemical reaction. And, because liquid physical blowing agents tend to be easier to ship, store, handle, and use, they are typically used more extensively (in rigid foam applications) than gaseous ones. Thus, liquid chlorofluorocarbons (CFC's) and hydrochlorofluorocarbons (HCFC's) have been widely used to produce closed-cell polyurethane foams with good thermal insulation and dimensional stability properties. However, CFC's and HCFC's have fallen into disfavor due to their ozone depletion potential (ODP) and to their global warming potential (GWP). Because of these concerns many countries have restricted, or will restrict, the use of CFC's and HCFC's.
Although blowing agents other than CFC's and HCFC's are available, they too have disadvantages. For example, both saturated hydrofluorocarbons (HFC's) and hydrocarbons (HC's) have zero ODP, but saturated HFC's have a relatively high GWP and HC's are highly flammable volatile organic compounds (VOCs). Thus, there are questions about the acceptability of long-term use of saturated HFC's, and, in at least some insulation applications, the cost associated with safe use and risk management of HC's can be prohibitive.
Perfluoroalkanes (alkanes where all hydrogen has been substituted by fluorine) and perfluoroalkenes are two other types of materials that have been evaluated as physical blowing agents. Perfluoroalkanes have an extremely high GWP, which has virtually eliminated their use as commercial foam blowing agents. Further, for different reasons, commercial use of perfluoroalkenes (as blowing agents in rigid polyurethane foams) is not widespread. For instance, perfluoroalkenes are expensive to make and they are not very soluble in components typically used to make polyurethane foams.
Promising physical blowing agents include various hydrogen-containing fluoroalkenes (as opposed to perfluoralkenes). These hydrofluoroalkenes may not have a substantial negative affect on atmospheric chemistry. For example, they may, by comparison to other halogenated blowing agents, contribute little to ozone depletion, and do not, by comparison to many saturated hydrofluorocarbon blowing agents, substantially contribute to global warming. But rigid polyurethane foams produced with such blowing agents (using known processes and reaction systems) do not have commercially attractive physical properties at low enough densities to make their use economically feasible. In short, the properties associated with such hydrofluoroalkene blown foams have generally been inferior to historic CFC and HCFC blown foams. Attempts to solve this problem have focused on making azeotropic blends with hydrofluoroalkenes. For instance, azeotropic blends have been made with hydrofluoroalkenes and at least one of another hydrofluoroalkene, saturated hydrofluorocarbons, hydrocarbons, trifluoroiodomethane, and other blowing agents. Such attempts have met with limited success.
Thus, there is a need for a reaction system including a blowing agent that does not substantially contribute to ozone depletion and global warming to make closed-cell rigid polyurethane foams and polyurethane-polyisocyanurate foams with good physical properties. The blowing agent of such reaction system should be normally liquid and should not be a volatile organic compound. Likewise, there is a need for methods of using such reaction systems and the foams produced therefrom.